1. Field of the Invention
The present invention relates to a zoom lens system in which a back focal distance can be short.
2. Description of the Related Art
In a zoom lens system in which a back focal distance can be short (e.g., a zoom lens system for a compact camera), there is no need to provide a longer back focal distance unlike a zoom lens system for a single lens reflex (SLR) camera, which requires a space for providing a mirror behind the photographing lens. Accordingly, a compact camera generally employs a telephoto type lens system in which positive and negative lens groups are provided in this order from the object side while a retrofocus type lens system, which includes negative and positive lens groups in this order from the object side, is generally employed in a SLR camera.
A telephoto two-lens group zoom lens system, which has a positive front lens group and a negative rear lens group, is simple, easy to adjust upon assembly, can reduce the number of lens elements, and is beneficial from the viewpoint of cost. However, in order to decrease the F-number at the long focal length extremity and to achieve high optical performance, aberration correction of the front lens group becomes the utmost importance, and the number of lens elements of the positive front lens group increases. Accordingly, the front lens group becomes heavy, so that the focusing mechanism has to bear a load.